©
National Instruments Corporation
3
SCXI-1322 Installation Guide
Do not substitute parts or modify equipment. Because of the danger of introducing
additional hazards, do not install unauthorized parts or modify the device. Return the
device to National Instruments for service and repair to ensure that its safety features are
not compromised.
When using the device with high common-mode voltages, you must insulate your signal
wires for the highest input voltage. National Instruments is not liable for any damages or
injuries resulting from inadequate signal wire insulation. Use only 26-14 AWG wire with
a voltage rating of 300 V and 60 °C for signals that may come in contact with 250 V;
use only 600 V and 60 °C wire for signals that may come in contact with 480 V.
When connecting or disconnecting signal lines to the SCXI terminal block screw terminals,
make sure the lines are powered off. Potential differences between the lines and the SCXI
ground create a shock hazard while you connect the lines.
Connections, including power signals to ground and vice versa, that exceed any of the
maximum signal ratings on the SCXI device can create a shock or fire hazard or can
damage any or all of the boards connected to the SCXI chassis, the host computer, and the
SCXI device. National Instruments is not liable for any damages or injuries resulting from
incorrect signal connections.
If high voltages (
≥
30 V
rms
and 42.4 V
peak
or 60 VDC) are present, you must connect a safety
earth ground wire to the terminal block safety ground solder lug, shown in Figure 1. This
complies with safety agency requirements and protects against electric shock when the
terminal block is not connected to the chassis. To connect the safety earth ground to the
safety ground solder lug, run an earth ground wire in the cable from the signal source to
the terminal block. National Instruments is not liable for any damages or injuries resulting
from inadequate safety earth ground connections.
Do not loosen or re-orient the safety ground solder lug hardware when connecting the
safety ground wire; to do so reduces the safety isolation between the high voltage and
safety ground.
Using the VEX/SENSE+ and the VEX/SENSE– Terminals
for Strain-Gauge Excitation
Your terminal block has two terminals labeled VEX/SENSE+ and
VEX/SENSE–. When resistors R3 and R4 are loaded (factory default), you
can use the VEX/SENSE+ and VEX/SENSE– terminals as VEX+ and
VEX– terminals, respectively. When you have a heavy load—for example,
all 16 channels are connected to 16 120
Ω
strain-gauge half-bridges—you
should remove resistors R3 and R4 to transform the VEX/SENSE+ and
VEX/SENSE– terminals to sense terminals. These terminals must connect
to the VEX+ and VEX– leads at the load for remote sensing and therefore
compensate for the voltage drop in the excitation leads.
Summary of Contents for SCXI-1322
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